Power quality indices have been developed to assess the performance of a single site or an entire system. They can guide utilities to improve their systems and can be used by manufacturers to decide about equipment immunity. This paper is the third part of a joint paper aimed at predicting the voltage sag performance of distribution networks by estimating voltage sag indices. Two types of indices are analyzed in the present paper, they give, respectively, the average number of events and the average interruption duration of each kilovolt ampere served at the low-voltage level over the assessment period. Their values are obtained from a stochastic prediction using a time-domain simulation tool. The methodology used to obtain these indices and the analysis of the influence of the protective devices are the main contributions of this paper. The limitations of the present work are also discussed.